D. Braun et al., DEFICITS AND RECOVERY OF FIRST-ORDER AND 2ND-ORDER MOTION PERCEPTION IN PATIENTS WITH UNILATERAL CORTICAL-LESIONS, European journal of neuroscience, 10(6), 1998, pp. 2117-2128
Unilateral lesions in the posterior parietal cortex can degrade motion
perception in the contralesional visual hemifield, Our aim was to inv
estigate whether deficits caused by cortical lesions may be different
for first-and second-order motion perception, and to study the time sc
ale of any potential recovery. In nine patients with circumscribed les
ions mainly in the parietal and fronto-parietal cortex, thresholds for
direction discrimination were measured for stimuli presented peripher
ally in their ipsi-and contralesional hemifield. Subjects had to ident
ify the direction of a vertically moving object embedded in a backgrou
nd of dynamic random dot noise. The object consisted of various propor
tions of signal and noise dots. Signal dots were either (a) coherently
moving in the same direction as the object (first-order), (b) station
ary (second-order: drift-balanced), or (c) coherently moving in the op
posite direction (second-order: theta). Noise dots were flickering. Tw
o patients showed significant threshold elevations for all three types
of motion stimuli presented in their contralesional hemifield, while
thresholds for ipsilesional targets were unaffected. Neither showed an
y selective deficit of first-versus second-order motion perception, bu
t second-order motion was more impaired. Their lesions probably includ
ed the motion area V5-MT, which was spared in the other seven patients
. One of the patients, who was retested several times during a 27-mont
h postlesional period, showed complete recovery for first-and second-o
rder motion direction discrimination, as well as for the detection of
speed differences.